Method and apparatus for dispersed storage memory device utilization

ABSTRACT

A method begins with a processing module receiving data for storage. The method continues with the processing module determining storage metadata regarding storage requirements of the data. When the storage metadata includes a first type of storage mode, the method continues with the processing module determining a first error coding dispersal storage function; identifying first memory of DSN memory; encoding the data in accordance with the first error coding dispersal storage functions; and outputting the first encoded data slices to the first memory for storage therein. When the storage metadata includes a second type of storage mode, the method continues with the processing module determining a second error coding dispersal storage function; identifying second memory of a dispersed storage network (DSN) memory; encoding the data in accordance with the second error coding dispersal storage functions; and outputting the second encoded data slices to the second memory for storage therein.

CROSS REFERENCE TO RELATED PATENTS

This patent application is claiming priority under 35 USC § 120 as acontinuing patent application of co-pending patent application entitled,“METHOD AND APPARATUS FOR DISPERSED STORAGE MEMORY DEVICE UTILIZATION”,having a filing date of May 12, 2010, and a Ser. No. 12/778,680, whichis incorporated herein by reference, and which claims priority under 35USC § 119 to a provisionally filed patent application entitled,“DISTRIBUTED STORAGE NETWORK MEMORY UTILIZATION”, having a provisionalfiling date of Sep. 30, 2009, and a provisional Ser. No. 61/247,190.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

NOT APPLICABLE

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

NOT APPLICABLE

BACKGROUND OF THE INVENTION

Technical Field of the Invention

This invention relates generally to computing systems and moreparticularly to data storage solutions within such computing systems.

Description of Related Art

Computers are known to communicate, process, and store data. Suchcomputers range from wireless smart phones to data centers that supportmillions of web searches, stock trades, or on-line purchases every day.In general, a computing system generates data and/or manipulates datafrom one form into another. For instance, an image sensor of thecomputing system generates raw picture data and, using an imagecompression program (e.g., JPEG, MPEG, etc.), the computing systemmanipulates the raw picture data into a standardized compressed image.

With continued advances in processing speed and communication speed,computers are capable of processing real time multimedia data forapplications ranging from simple voice communications to streaming highdefinition video. As such, general-purpose information appliances arereplacing purpose-built communications devices (e.g., a telephone). Forexample, smart phones can support telephony communications but they arealso capable of text messaging and accessing the internet to performfunctions including email, web browsing, remote applications access, andmedia communications (e.g., telephony voice, image transfer, musicfiles, video files, real time video streaming. etc.).

Each type of computer is constructed and operates in accordance with oneor more communication, processing, and storage standards. As a result ofstandardization and with advances in technology, more and moreinformation content is being converted into digital formats. Forexample, more digital cameras are now being sold than film cameras, thusproducing more digital pictures. As another example, web-basedprogramming is becoming an alternative to over the air televisionbroadcasts and/or cable broadcasts. As further examples, papers, books,video entertainment, home video, etc. are now being stored digitally,which increases the demand on the storage function of computers.

A typical computer storage system includes one or more memory devicesaligned with the needs of the various operational aspects of thecomputer's processing and communication functions. Generally, theimmediacy of access dictates what type of memory device is used. Forexample, random access memory (RAM) memory can be accessed in any randomorder with a constant response time, thus it is typically used for cachememory and main memory. By contrast, memory device technologies thatrequire physical movement such as magnetic disks, tapes, and opticaldiscs, have a variable response time as the physical movement can takelonger than the data transfer, thus they are typically used forsecondary memory (e.g., hard drive, backup memory, etc.).

A computer's storage system will be compliant with one or more computerstorage standards that include, but are not limited to, network filesystem (NFS), flash file system (FFS), disk file system (DFS), smallcomputer system interface (SCSI), internet small computer systeminterface (iSCSI), file transfer protocol (FTP), and web-baseddistributed authoring and versioning (WebDAV). These standards specifythe data storage format (e.g., files, data objects, data blocks,directories, etc.) and interfacing between the computer's processingfunction and its storage system, which is a primary function of thecomputer's memory controller.

Despite the standardization of the computer and its storage system,memory devices fail; especially commercial grade memory devices thatutilize technologies incorporating physical movement (e.g., a discdrive). For example, it is fairly common for a disc drive to routinelysuffer from bit level corruption and to completely fail after threeyears of use. One solution is to utilize a higher-grade disc drive,which adds significant cost to a computer.

Another solution is to utilize multiple levels of redundant disc drivesto replicate the data into two or more copies. One such redundant driveapproach is called redundant array of independent discs (RAID). In aRAID device, a RAID controller adds parity data to the original databefore storing it across the array. The parity data is calculated fromthe original data such that the failure of a disc will not result in theloss of the original data. For example, RAID 5 uses three discs toprotect data from the failure of a single disc. The parity data, andassociated redundancy overhead data, reduces the storage capacity ofthree independent discs by one third (e.g., n−1=capacity). RAID 6 canrecover from a loss of two discs and requires a minimum of four discswith a storage capacity of n−2.

While RAID addresses the memory device failure issue, it is not withoutits own failure issues that affect its effectiveness, efficiency andsecurity. For instance, as more discs are added to the array, theprobability of a disc failure increases, which increases the demand formaintenance. For example, when a disc fails, it needs to be manuallyreplaced before another disc fails and the data stored in the RAIDdevice is lost. To reduce the risk of data loss, data on a RAID deviceis typically copied on to one or more other RAID devices. While thisaddresses the loss of data issue, it raises a security issue sincemultiple copies of data are available, which increases the chances ofunauthorized access. Further, as the amount of data being stored grows,the overhead of RAID devices becomes a non-trivial efficiency issue.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is a schematic block diagram of an embodiment of a computingsystem in accordance with the invention;

FIG. 2 is a schematic block diagram of an embodiment of a computing corein accordance with the invention;

FIG. 3 is a schematic block diagram of an embodiment of a distributedstorage processing module in accordance with the invention;

FIG. 4 is a schematic block diagram of an embodiment of a grid module inaccordance with the invention;

FIG. 5 is a diagram of an example embodiment of error coded data slicecreation in accordance with the invention;

FIG. 6 is a schematic block diagram of another embodiment of a computingsystem in accordance with the invention;

FIG. 7 is a flowchart of an embodiment of a method for determining datadistribution in accordance with the present invention;

FIG. 8 is another flowchart of another embodiment of a method fordetermining data distribution in accordance with the present invention;

FIG. 9 is a schematic block diagram of an embodiment of a distributedstorage unit in accordance with the invention;

FIG. 10 is a flowchart of another embodiment of a method for determiningdata distribution in accordance with the present invention; and

FIG. 11 is a flowchart of an embodiment of a method for memory devicemanagement in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic block diagram of a computing system 10 thatincludes one or more of a first type of user devices 12, one or more ofa second type of user devices 14, at least one distributed storage (DS)processing unit 16, at least one DS managing unit 18, at least onestorage integrity processing unit 20, and a distributed storage network(DSN) memory 22 coupled via a network 24. The network 24 may include oneor more wireless and/or wire lined communication systems; one or moreprivate intranet systems and/or public internet systems; and/or one ormore local area networks (LAN) and/or wide area networks (WAN).

The DSN memory 22 includes a plurality of distributed storage (DS) units36 for storing data of the system. Each of the DS units 36 includes aprocessing module and memory and may be located at a geographicallydifferent site than the other DS units (e.g., one in Chicago, one inMilwaukee, etc.). The processing module may be a single processingdevice or a plurality of processing devices. Such a processing devicemay be a microprocessor, micro-controller, digital signal processor,microcomputer, central processing unit, field programmable gate array,programmable logic device, state machine, logic circuitry, analogcircuitry, digital circuitry, and/or any device that manipulates signals(analog and/or digital) based on hard coding of the circuitry and/oroperational instructions. The processing module may have an associatedmemory and/or memory element, which may be a single memory device, aplurality of memory devices, and/or embedded circuitry of the processingmodule. Such a memory device may be a read-only memory, random accessmemory, volatile memory, non-volatile memory, static memory, dynamicmemory, flash memory, cache memory, and/or any device that storesdigital information. Note that if the processing module includes morethan one processing device, the processing devices may be centrallylocated (e.g., directly coupled together via a wired and/or wireless busstructure) or may be distributedly located (e.g., cloud computing viaindirect coupling via a local area network and/or a wide area network).Further note that when the processing module implements one or more ofits functions via a state machine, analog circuitry, digital circuitry,and/or logic circuitry, the memory and/or memory element storing thecorresponding operational instructions may be embedded within, orexternal to, the circuitry comprising the state machine, analogcircuitry, digital circuitry, and/or logic circuitry. Still further notethat, the memory element stores, and the processing module executes,hard coded and/or operational instructions corresponding to at leastsome of the steps and/or functions illustrated in FIGS. 1-9.

Each of the user devices 12-14, the DS processing unit 16, the DSmanaging unit 18, and the storage integrity processing unit 20 may be aportable computing device (e.g., a social networking device, a gamingdevice, a cell phone, a smart phone, a personal digital assistant, adigital music player, a digital video player, a laptop computer, ahandheld computer, a video game controller, and/or any other portabledevice that includes a computing core) and/or a fixed computing device(e.g., a personal computer, a computer server, a cable set-top box, asatellite receiver, a television set, a printer, a fax machine, homeentertainment equipment, a video game console, and/or any type of homeor office computing equipment). Such a portable or fixed computingdevice includes a computing core 26 and one or more interfaces 30, 32,and/or 33. An embodiment of the computing core 26 will be described withreference to FIG. 2.

With respect to the interfaces, each of the interfaces 30, 32, and 33includes software and/or hardware to support one or more communicationlinks via the network 24 and/or directly. For example, interface 30supports a communication link (wired, wireless, direct, via a LAN, viathe network 24, etc.) between the first type of user device 14 and theDS processing unit 16. As another example, DSN interface 32 supports aplurality of communication links via the network 24 between the DSNmemory 22 and the DS processing unit 16, the first type of user device12, and/or the storage integrity processing unit 20. As yet anotherexample, interface 33 supports a communication link between the DSmanaging unit 18 and any one of the other devices and/or units 12, 14,16, 20, and/or 22 via the network 24.

In general and with respect to data storage, the system 10 supportsthree primary functions: distributed network data storage management,distributed data storage and retrieval, and data storage integrityverification. In accordance with these three primary functions, data canbe distributedly stored in a plurality of physically different locationsand subsequently retrieved in a reliable and secure manner regardless offailures of individual storage devices, failures of network equipment,the duration of storage, the amount of data being stored, attempts athacking the data, etc.

The DS managing unit 18 performs distributed network data storagemanagement functions, which include establishing distributed datastorage parameters, performing network operations, performing networkadministration, and/or performing network maintenance. The DS managingunit 18 establishes the distributed data storage parameters (e.g.,allocation of virtual DSN memory space, distributed storage parameters,security parameters, billing information, user profile information,etc.) for one or more of the user devices 12-14 (e.g., established forindividual devices, established for a user group of devices, establishedfor public access by the user devices, etc.). For example, the DSmanaging unit 18 coordinates the creation of a vault (e.g., a virtualmemory block) within the DSN memory 22 for a user device (for a group ofdevices, or for public access). The DS managing unit 18 also determinesthe distributed data storage parameters for the vault. In particular,the DS managing unit 18 determines a number of slices (e.g., the numberthat a data segment of a data file and/or data block is partitioned intofor distributed storage) and a read threshold value (e.g., the minimumnumber of slices required to reconstruct the data segment).

As another example, the DS managing unit 18 creates and stores, locallyor within the DSN memory 22, user profile information. The user profileinformation includes one or more of authentication information,permissions, and/or the security parameters. The security parameters mayinclude one or more of encryption/decryption scheme, one or moreencryption keys, key generation scheme, and data encoding/decodingscheme.

As yet another example, the DS managing unit 18 creates billinginformation for a particular user, user group, vault access, publicvault access, etc. For instance, the DS managing unit 18 tracks thenumber of times a user accesses a private vault and/or public vaults,which can be used to generate a per-access bill. In another instance,the DS managing unit 18 tracks the amount of data stored and/orretrieved by a user device and/or a user group, which can be used togenerate a per-data-amount bill.

The DS managing unit 18 also performs network operations, networkadministration, and/or network maintenance. As at least part ofperforming the network operations and/or administration, the DS managingunit 18 monitors performance of the devices and/or units of the system10 for potential failures, determines the devices' and/or units'activation status, determines the devices' and/or units' loading, andany other system level operation that affects the performance level ofthe system 10. For example, the DS managing unit 18 receives andaggregates network management alarms, alerts, errors, statusinformation, performance information, and messages from the devices12-14 and/or the units 16, 20, 22. For example, the DS managing unit 18receives a simple network management protocol (SNMP) message regardingthe status of the DS processing unit 16.

The DS managing unit 18 performs the network maintenance by identifyingequipment within the system 10 that needs replacing, upgrading,repairing, and/or expanding. For example, the DS managing unit 18determines that the DSN memory 22 needs more DS units 36 or that one ormore of the DS units 36 needs updating.

The second primary function (i.e., distributed data storage andretrieval) begins and ends with a user device 12-14. For instance, if asecond type of user device 14 has a data file 38 and/or data block 40 tostore in the DSN memory 22, it sends the data file 38 and/or data block40 to the DS processing unit 16 via its interface 30. As will bedescribed in greater detail with reference to FIG. 2, the interface 30functions to mimic a conventional operating system (OS) file systeminterface (e.g., network file system (NFS), flash file system (FFS),disk file system (DFS), file transfer protocol (FTP), web-baseddistributed authoring and versioning (WebDAV), etc.) and/or a blockmemory interface (e.g., small computer system interface (SCSI), internetsmall computer system interface (iSCSI), etc.). In addition, theinterface 30 may attach a user identification code (ID) to the data file38 and/or data block 40.

The DS processing unit 16 receives the data file 38 and/or data block 40via its interface 30 and performs a distributed storage (DS) process 34thereon (e.g., an error coding dispersal storage function). The DSprocessing 34 begins by partitioning the data file 38 and/or data block40 into one or more data segments, which is represented as Y datasegments. For example, the DS processing 34 may partition the data file38 and/or data block 40 into a fixed byte size segment (e.g., 2¹ to2^(n) bytes, where n=>2) or a variable byte size (e.g., change byte sizefrom segment to segment, or from groups of segments to groups ofsegments, etc.).

For each of the Y data segments, the DS processing 34 error encodes(e.g., forward error correction (FEC), information dispersal algorithm,or error correction coding) and slices (or slices then error encodes)the data segment into a plurality of error coded (EC) data slices 42-48,which is represented as X slices per data segment. The number of slices(X) per segment, which corresponds to a number of pillars n, is set inaccordance with the distributed data storage parameters and the errorcoding scheme. For example, if a Reed-Solomon (or other FEC scheme) isused in an n/k system, then a data segment is divided into n slices,where k number of slices is needed to reconstruct the original data(i.e., k is the threshold). As a few specific examples, the n/k factormay be 5/3; 6/4; 8/6; 8/5; 16/10.

For each EC slice 42-48, the DS processing unit 16 creates a uniqueslice name and appends it to the corresponding EC slice 42-48. The slicename includes universal DSN memory addressing routing information (e.g.,virtual memory addresses in the DSN memory 22) and user-specificinformation (e.g., user ID, file name, data block identifier, etc.).

The DS processing unit 16 transmits the plurality of EC slices 42-48 toa plurality of DS units 36 of the DSN memory 22 via the DSN interface 32and the network 24. The DSN interface 32 formats each of the slices fortransmission via the network 24. For example, the DSN interface 32 mayutilize an internet protocol (e.g., TCP/IP, etc.) to packetize the ECslices 42-48 for transmission via the network 24.

The number of DS units 36 receiving the EC slices 42-48 is dependent onthe distributed data storage parameters established by the DS managingunit 18. For example, the DS managing unit 18 may indicate that eachslice is to be stored in a different DS unit 36. As another example, theDS managing unit 18 may indicate that like slice numbers of differentdata segments are to be stored in the same DS unit 36. For example, thefirst slice of each of the data segments is to be stored in a first DSunit 36, the second slice of each of the data segments is to be storedin a second DS unit 36, etc. In this manner, the data is encoded anddistributedly stored at physically diverse locations to improve datastorage integrity and security. Further examples of encoding the datasegments will be provided with reference to one or more of FIGS. 2-9.

Each DS unit 36 that receives an EC slice 42-48 for storage translatesthe virtual DSN memory address of the slice into a local physicaladdress for storage. Accordingly, each DS unit 36 maintains a virtual tophysical memory mapping to assist in the storage and retrieval of data.

The first type of user device 12 performs a similar function to storedata in the DSN memory 22 with the exception that it includes the DSprocessing. As such, the device 12 encodes and slices the data fileand/or data block it has to store. The device then transmits the slices35 to the DSN memory via its DSN interface 32 and the network 24.

For a second type of user device 14 to retrieve a data file or datablock from memory, it issues a read command via its interface 30 to theDS processing unit 16. The DS processing unit 16 performs the DSprocessing 34 to identify the DS units 36 storing the slices of the datafile and/or data block based on the read command. The DS processing unit16 may also communicate with the DS managing unit 18 to verify that theuser device 14 is authorized to access the requested data.

Assuming that the user device is authorized to access the requesteddata, the DS processing unit 16 issues slice read commands to at least athreshold number of the DS units 36 storing the requested data (e.g., toat least 10 DS units for a 16/10 error coding scheme). Each of the DSunits 36 receiving the slice read command, verifies the command,accesses its virtual to physical memory mapping, retrieves the requestedslice, or slices, and transmits it to the DS processing unit 16.

Once the DS processing unit 16 has received a read threshold number ofslices for a data segment, it performs an error decoding function andde-slicing to reconstruct the data segment. When Y number of datasegments has been reconstructed, the DS processing unit 16 provides thedata file 38 and/or data block 40 to the user device 14. Note that thefirst type of user device 12 performs a similar process to retrieve adata file and/or data block.

The storage integrity processing unit 20 performs the third primaryfunction of data storage integrity verification. In general, the storageintegrity processing unit 20 periodically retrieves slices 45, and/orslice names, of a data file or data block of a user device to verifythat one or more slices have not been corrupted or lost (e.g., the DSunit failed). The retrieval process mimics the read process previouslydescribed.

If the storage integrity processing unit 20 determines that one or moreslices is corrupted or lost, it rebuilds the corrupted or lost slice(s)in accordance with the error coding scheme. The storage integrityprocessing unit 20 stores the rebuilt slice, or slices, in theappropriate DS unit(s) 36 in a manner that mimics the write processpreviously described.

FIG. 2 is a schematic block diagram of an embodiment of a computing core26 that includes a processing module 50, a memory controller 52, mainmemory 54, a video graphics processing unit 55, an input/output (IO)controller 56, a peripheral component interconnect (PCI) interface 58,an IO interface 60, at least one IO device interface module 62, a readonly memory (ROM) basic input output system (BIOS) 64, and one or morememory interface modules. The memory interface module(s) includes one ormore of a universal serial bus (USB) interface module 66, a host busadapter (HBA) interface module 68, a network interface module 70, aflash interface module 72, a hard drive interface module 74, and a DSNinterface module 76. Note the DSN interface module 76 and/or the networkinterface module 70 may function as the interface 30 of the user device14 of FIG. 1. Further note that the IO device interface module 62 and/orthe memory interface modules may be collectively or individuallyreferred to as IO ports.

The processing module 50 may be a single processing device or aplurality of processing devices. Such a processing device may be amicroprocessor, micro-controller, digital signal processor,microcomputer, central processing unit, field programmable gate array,programmable logic device, state machine, logic circuitry, analogcircuitry, digital circuitry, and/or any device that manipulates signals(analog and/or digital) based on hard coding of the circuitry and/oroperational instructions. The processing module 50 may have anassociated memory and/or memory element, which may be a single memorydevice, a plurality of memory devices, and/or embedded circuitry of theprocessing module 50. Such a memory device may be a read-only memory,random access memory, volatile memory, non-volatile memory, staticmemory, dynamic memory, flash memory, cache memory, and/or any devicethat stores digital information. Note that if the processing module 50includes more than one processing device, the processing devices may becentrally located (e.g., directly coupled together via a wired and/orwireless bus structure) or may be distributedly located (e.g., cloudcomputing via indirect coupling via a local area network and/or a widearea network). Further note that when the processing module 50implements one or more of its functions via a state machine, analogcircuitry, digital circuitry, and/or logic circuitry, the memory and/ormemory element storing the corresponding operational instructions may beembedded within, or external to, the circuitry comprising the statemachine, analog circuitry, digital circuitry, and/or logic circuitry.Still further note that, the memory element stores, and the processingmodule 50 executes, hard coded and/or operational instructionscorresponding to at least some of the steps and/or functions illustratedin FIGS. 1-9.

FIG. 3 is a schematic block diagram of an embodiment of a dispersedstorage (DS) processing module 34 of user device 12 and/or of the DSprocessing unit 16. The DS processing module 34 includes a gatewaymodule 78, an access module 80, a grid module 82, and a storage module84. The DS processing module 34 may also include an interface 30 and theDSnet interface 32 or the interfaces 68 and/or 70 may be part of userdevice 12 or of the DS processing unit 16. The DS processing module 34may further include a bypass/feedback path between the storage module 84to the gateway module 78.

In an example of storing data, the gateway module 78 receives anincoming data object (e.g., a data file, a data block, an EC data slice,etc.) that includes a user ID field 86, an object name field 88, and thedata field 40. The gateway module 78 authenticates the user associatedwith the data object by verifying the user ID 86 with the managing unit18 and/or another authenticating unit. When the user is authenticated,the gateway module 78 obtains user information from the management unit18, the user device, and/or the other authenticating unit. The userinformation includes a vault identifier, operational parameters, anduser attributes (e.g., user data, billing information, etc.). A vaultidentifier identifies a vault, which is a virtual memory space that mapsto a set of DS storage units 36. For example, vault 1 (i.e., user 1'sDSN memory space) includes eight DS storage units (X=8 wide) and vault 2(i.e., user 2's DSN memory space) includes sixteen DS storage units(X=16 wide). The operational parameters may include an error codingalgorithm, the width n (number of pillars X or slices per segment forthis vault), a read threshold T, an encryption algorithm, a slicingparameter, a compression algorithm, an integrity check method, cachingsettings, parallelism settings, and/or other parameters that may be usedto access the DSN memory layer.

The gateway module 78 uses the user information to assign a source nameto the data. For instance, the gateway module 78 determines the sourcename of the data object 40 based on the vault identifier and the dataobject. For example, the source name may contain a data name (blocknumber or a file number), the vault generation number, the reservedfield, and the vault identifier. The data name may be randomly assignedbut is associated with the user data object.

The access module 62 receives the data object 40 and creates a series ofdata segments 1 through Y 90-92 therefrom. The number of segments Y maybe chosen or randomly assigned based on a selected segment size and thesize of the data object. For example, if the number of segments ischosen to be a fixed number, then the size of the segments varies as afunction of the size of the data object. For instance, if the dataobject is an image file of 4,194,304 eight bit bytes (e.g., 33,554,432bits) and the number of segments Y=131,072, then each segment is 256bits or 32 bytes. As another example, if segment size is fixed, then thenumber of segments Y varies based on the size of data object. Forinstance, if the data object is an image file of 4,194,304 bytes and thefixed size of each segment is 4,096 bytes, then the number of segmentsY=1,024. Note that each segment is associated with the source name.

The grid module 82 may pre-manipulate (e.g., compression, encryption,cyclic redundancy check (CRC), etc.) each of the data segments beforeperforming an error coding function of the error coding dispersalstorage function to produce a pre-manipulated data segment. The gridmodule 82 then error encodes (e.g., Reed-Solomon, Convolution encoding,Trellis encoding, etc.) the data segment or pre-manipulated data segmentinto X error coded data slices 42-44. The grid module 64 determines aunique slice name for each error coded data slice and attaches it to thedata slice.

The value X, or the number of pillars (e.g., X=16), is chosen as aparameter of the error coding dispersal storage function. Otherparameters of the error coding dispersal function include a readthreshold T, a write threshold W, etc. The read threshold (e.g., T=10,when X=16) corresponds to the minimum number of error-free error codeddata slices required to reconstruct the data segment. In other words,the DS processing module 34 can compensate for X-T (e.g., 16−10=6)missing error coded data slices per data segment. The write threshold Wcorresponds to a minimum number of DS storage units that acknowledgeproper storage of their respective data slices before the DS processingmodule indicates proper storage of the encoded data segment. Note thatthe write threshold is greater than or equal to the read threshold for agiven number of pillars (X).

The grid module 82 also determines which of the DS storage units 36 willstore the EC data slices based on a dispersed storage memory mappingassociated with the user's vault and/or DS storage unit 36 attributes.The DS storage unit attributes includes availability, self-selection,performance history, link speed, link latency, ownership, available DSNmemory, domain, cost, a prioritization scheme, a centralized selectionmessage from another source, a lookup table, data ownership, and/or anyother factor to optimize the operation of the computing system. Notethat the number of DS storage units 36 is equal to or greater than thenumber of pillars (e.g., X) so that no more than one error coded dataslice of the same data segment is stored on the same DS storage unit 36.Further note that EC data slices of the same pillar number but ofdifferent segments (e.g., EC data slice 1 of data segment 1 and EC dataslice 1 of data segment 2) may be stored on the same or different DSstorage units 36.

The storage module 84 performs an integrity check on the EC data slicesand, when successful, transmits the EC data slices 1 through X of eachsegment 1 through Y to the DS Storage units. Each of the DS storageunits 36 stores its EC data slice and keeps a table to convert thevirtual DSN address of the EC data slice into physical storageaddresses.

In an example of a read operation, the user device 12 and/or 14 sends aread request to the DS processing unit 16, which authenticates therequest. When the request is authentic, the DS processing unit 16 sendsa read message to each of the DS storage units 36 storing slices of thedata object being read. The slices are received via the DSnet interface32 and processed by the storage module 84, which performs a parity checkand provides the slices to the grid module 82 when the parity check wassuccessful. The grid module 82 decodes the slices in accordance with theerror coding dispersal storage function to reconstruct the data segment.The access module 80 reconstructs the data object from the data segmentsand the gateway module 78 formats the data object for transmission tothe user device.

FIG. 4 is a schematic block diagram of an embodiment of a grid module 82that includes a control unit 73, a pre-data manipulator 75, an encoder77, a slicer 79, a post-data manipulator 81, a pre-data de-manipulator83, a decoder 85, a de-slicer 87, and/or a post-data de-manipulator 89.Note that the control unit 73 may be partially or completely external tothe grid module 82. For example, the control unit 73 may be part of thecomputing core at a remote location, part of a user device, part of theDS managing unit 18, or distributed amongst one or more DS storageunits.

In an example of write operation, the pre-data manipulator 75 receives adata segment 90-92 and a write instruction from an authorized userdevice. The pre-data manipulator 75 determines if pre-manipulation ofthe data segment 90-92 is required and, if so, what type. The pre-datamanipulator 75 may make the determination independently or based oninstructions from the control unit 73, where the determination is baseda computing system-wide predetermination, a table lookup, vaultparameters associated with the user identification, the type of data,security requirements, available DSN memory, performance requirements,and/or other metadata.

Once a positive determination is made, the pre-data manipulator 75manipulates the data segment 90-92 in accordance with the type ofmanipulation. For example, the type of manipulation may be compression(e.g., Lempel-Ziv-Welch, Huffman, Golomb, fractal, wavelet, etc.),signatures (e.g., Digital Signature Algorithm (DSA), Elliptic Curve DSA,Secure Hash Algorithm, etc.), watermarking, tagging, encryption (e.g.,Data Encryption Standard, Advanced Encryption Standard, etc.), addingmetadata (e.g., time/date stamping, user information, file type, etc.),cyclic redundancy check (e.g., CRC32), and/or other data manipulationsto produce the pre-manipulated data segment.

The encoder 77 encodes the pre-manipulated data segment 92 using aforward error correction (FEC) encoder (and/or other type of erasurecoding and/or error coding) to produce an encoded data segment 94. Theencoder 77 determines which forward error correction algorithm to usebased on a predetermination associated with the user's vault, a timebased algorithm, user direction, DS managing unit direction, controlunit direction, as a function of the data type, as a function of thedata segment 92 metadata, and/or any other factor to determine algorithmtype. The forward error correction algorithm may be Golay,Multidimensional parity, Reed-Solomon, Hamming, Bose Ray ChauduriHocquenghem (BCH), Cauchy-Reed-Solomon, or any other FEC encoder. Notethat the encoder 77 may use a different encoding algorithm for each datasegment 92, the same encoding algorithm for the data segments 92 of adata object, or a combination thereof.

The encoded data segment 94 is of greater size than the data segment 92by the overhead rate of the encoding algorithm by a factor of d*(X/T),where d is size of the data segment 92, X is the width or number ofslices, and T is the read threshold. In this regard, the correspondingdecoding process can accommodate at most X−T missing EC data slices andstill recreate the data segment 92. For example, if X=16 and T=10, thenthe data segment 92 will be recoverable as long as 10 or more EC dataslices per segment are not corrupted.

The slicer 79 transforms the encoded data segment 94 into EC data slicesin accordance with the slicing parameter from the vault for this userand/or data segment 92. For example, if the slicing parameter is X=16,then the slicer slices each encoded data segment 94 into 16 encodedslices.

The post-data manipulator 81 performs, if enabled, post-manipulation onthe encoded slices to produce the EC data slices. If enabled, thepost-data manipulator 81 determines the type of post-manipulation, whichmay be based on a computing system-wide predetermination, parameters inthe vault for this user, a table lookup, the user identification, thetype of data, security requirements, available DSN memory, performancerequirements, control unit directed, and/or other metadata. Note thatthe type of post-data manipulation may include slice level compression,signatures, encryption, CRC, addressing, watermarking, tagging, addingmetadata, and/or other manipulation to improve the effectiveness of thecomputing system.

In an example of a read operation, the post-data de-manipulator 89receives at least a read threshold number of EC data slices and performsthe inverse function of the post-data manipulator 81 to produce aplurality of encoded slices. The de-slicer 87 de-slices the encodedslices to produce an encoded data segment 94. The decoder 85 performsthe inverse function of the encoder 77 to recapture the data segment90-92. The pre-data de-manipulator 83 performs the inverse function ofthe pre-data manipulator 75 to recapture the data segment.

FIG. 5 is a diagram of an example of slicing an encoded data segment 94by the slicer 79. In this example, the encoded data segment includesthirty-two bits, but may include more or less bits. The slicer 79disperses the bits of the encoded data segment 94 across the EC dataslices in a pattern as shown. As such, each EC data slice does notinclude consecutive bits of the data segment 94 reducing the impact ofconsecutive bit failures on data recovery. For example, if EC data slice2 (which includes bits 1, 5, 9, 13, 17, 25, and 29) is unavailable(e.g., lost, inaccessible, or corrupted), the data segment can bereconstructed from the other EC data slices (e.g., 1, 3 and 4 for a readthreshold of 3 and a width of 4).

FIG. 6 is a schematic block diagram of the DS processing module 34operably coupled (e.g., via one or more networks) to a plurality of DSN(dispersed storage network) memory sites (e.g., DSN memory 1, a DSNmemory 2, and a DSN memory 3) of the DSN memory 22. In this example, DSNmemory site 1 includes one or more DS units 94-96 utilizing a memory A;DSN memory site 2 includes at least one DS unit 98 utilizing the memoryA and at least one DS unit utilizing a memory B 100; and DSN memory site3 includes at least one DS unit 102-104 utilizing the memory A and thememory B. Memory A and memory B have different memory characteristics,which are known to the DS processing module 34 and/or to the DS units94-104. The memory characteristics may include speed of access, cost,reliability, availability, capacity and other parameters. Note that DSunits 94-104 correspond to DS units 36 of FIG. 1.

In an example of operation, the DS processing module 34 has a dataobject to store and determines (e.g., looks up, receives, retrieves frommemory, etc.) storage metadata for the data object. The storage metadataincludes storage requirements for the data object. The storagerequirements include one or more of: a file type, file size, priority,security index, estimated storage time, estimated time betweenretrievals and more.

The DS processing module 34 then determines (e.g., looks up, receives,retrieves from memory, etc.) memory device capabilities of the DSNmemory 22. The memory device capabilities include a memory devicestorage cost, a memory device storage access speed, a memory devicestorage reliability, a memory device storage availability, and/or amemory device storage capacity. In this example, memory A has differentmemory device capabilities than memory B. For example, memory B may havea faster access speed than memory A.

The DS processing module 34 then identifies memory devices of the DSNmemory based on the memory device capabilities and the storage metadatato produce identified memory devices. For example, the DS processingmodule 34 interprets the storage requirements of the metadata andattempts to match the requirements with the memory device capabilities.As a specific example, if the data object has a storage requirement fora fast access time, then the DS processing module would identify memoryB for storage (as opposed to memory A in this example, which has aslower access time).

The DS processing module then encodes the data into a plurality of dataslices in accordance with an error coding dispersal function and outputsthe data slices to the identified memory devices for storage. Forexample, the slices are outputted to DS units 100-104 for storage inmemory B.

In another example of operation, the DS processing unit 16 considersmoving the previously stored data object and may choose to move the dataobject slices from one memory type to another (e.g., from memory B tomemory A). In this instance, the DS processing module 34 interprets thestorage metadata, which indicates that a fast data retrieval is nolonger required, and initiates the data transfer. The data transfer maybe a straight transfer of the data slices from memory B to memory A, ormay be done by reconstructing the data object from the slices in memoryB, re-encode the reconstructed data object using the same or differentoperational parameters of the error coding dispersal storage function toproduce re-constructed slices, and storing the reconstructed slices inmemory A.

FIG. 7 is a flowchart illustrating the determination of a datadistribution method where the DS processing unit may choose the memory,create the slices, and send the slices for storage to the chosen memory.The method begins at step 106 where the DS processing module receives adata object from a source (e.g., a user device, the storage integrityprocessing unit, another DS processing unit, the DS unit, and/or the DSmanaging unit).

The method continues at step 108 where the DS processing moduledetermines the storage metadata (e.g., a file type, file size, priority,security index, estimated storage time, estimated time betweenretrievals, etc.) associated with the data object. Such a determinationis based on one or more of the data, information received with the data,information derived from generation of the data, a command, a message,and/or a predetermination. Alternatively, or in addition to, thedetermination may be based on segmenting the data in accordance with anerror coding dispersal function to produce a plurality of data segmentsfollowed by subsequent determination of the storage metadata based on atleast one of the plurality of data segments. As yet another alternativeor addition, the determination may be based on partitioning the databased on customized data content (e.g., user preferences and/or files)and generic data content (e.g., a commonly available application) toproduce a customized data partition and a generic data partitionfollowed by the subsequent determination of customized data partitionstorage metadata regarding the customized data partition and genericdata partition storage metadata regarding the generic data partitionfollowed by aggregation of the customized data partition storagemetadata and the generic data partition storage metadata to produce thestorage metadata.

The method continues at step 110 where the DS processing unit determinesa storage dispersal method (e.g., operational parameters for an errorcoding dispersal storage function). The operational parameters includeone or more of: a pillar width, a read threshold, an error codingalgorithm, an encryption algorithm, a slicing parameter, a compressionalgorithm, an integrity check method, a caching settings, and aparallelism settings. Within step 110, the DS processing module encodesthe data segment in accordance with the storage dispersal method toproduce a plurality of error coded data slices (which may also bereferred to as data slices or slices). For example, the metadata mayrequire high reliability and fast retrieval speeds for a near term timeperiod. In this example, the DS processing unit would select a storagedispersal method to include a low number pillars (e.g., X) using acertain type of memory device to speed subsequent retrieval.

The method continues at step 112 where the DS processing moduledetermines a storage mode based on the metadata and memory capabilitiesof the DSN memory. The storage mode includes a memory selection and mayfurther include a time phase indicator. The time phase indicatorspecifies one or more time intervals for a given set of storagerequirements. For example, the time phase indicator specifies a firsttime phase that corresponds to a time period from the initial storage ofthe new data object and second time phase that corresponds to the timeperiod after the first time phase expires. As a specific example, the DSprocessing unit determines the storage mode to be a B mode (e.g., fastreliable and costly solid state memory) for the first time phase andstorage mode A for the second time phase.

The DS processing module may also determine the storage mode based onthe type of data. For example, the data may include customized datacontent (e.g., user preferences and/or files) and/or generic datacontent (e.g., a commonly available application). In this example, thegeneric data content may have one type of storage mode (e.g., slower,less reliable, etc.), while the customized data content may have anothertype of storage mode (e.g., faster, more reliable, etc.).

The method continues at step 114 where the DS processing unit utilizesthe current storage mode to store slices in the DSN memory. In thisinstance, the DS processing unit looks up the mapping in the virtual DSNaddress to physical location table to determine where the slices shouldbe stored. Note that the virtual DSN address to physical location tablemay include both the current storage mode and the last storage mode tofacilitate moving slices from the memory of the last mode to the memoryin accordance with the current storage mode.

When the storage mode is mode B, the method continues to step 116 wherethe DS processing module sends the data slices to DS units with memorytype B. When the storage mode is mode A, the method continues to step122 where the DS processing sends the data slices to DS units withmemory type A. Note that such decisions may be made on a data segment bydata segment basis or for groupings of data segments (e.g., a datafile).

When the storage mode is mode A/B, the method continues at step 118where the DS processing module sends k slices to DS units with memorytype B 118 and, at step 120, sends the other n−k slices to DS units withmemory type A. Note that this scenario may include themetadata-indicated requirement for fast access (without failures),reliable memory with some cost constraint for the current time phase.Further note that when k is equal to or is greater than the readthreshold, the DS processing unit can retrieve slices from the memory Bwithout retrieving slices from memory A unless one or more slices frommemory B is missing or corrupt.

After storing the slices, the method continues at step 124 where the DSprocessing module determines whether it is time to reassess the storagemode. Such a determination may be based on one or more of a time periodhas elapsed since the current storage mode, there have been noretrievals of the data object within a time period, a command, arequest, and/or a memory type is filling up (e.g., memory B). Note thata likely scenario is starting with the B mode (e.g., fast and frequentdata retrievals), transition to the A/B mode (e.g., less frequent, butstill fast data retrievals), and then transition and remain at in mode A(e.g., less frequent and slower data retrievals).

Alternatively, or in addition to, the reassessing may be based on theoccurrence of a condition to update the identification of the memorydevices. The condition may include one or more of, but not limited to,updating of the storage metadata, a change of memory devicecharacteristics, a change of available memory devices, and/or anoccurrence of a triggering event. For example, the processing module maydetermine that the condition has occurred to update the dedication ofthe memory devices when new memory devices with more favorable memorycharacteristics relative to the storage requirements are available areathe method continues with the step where the processing modulere-identifies memory devices when the condition has occurred. In such aninstance, the processing module may retrieve a portion of the pluralityof data slices and facilitate moving the plurality of data slices to there-identified memory devices.

If not reassessing, the method repeats at step 114. If reassessing, themethod continues step 112 where the DS processing unit determineswhether to change the storage mode. Such a change may be to move fromstorage mode B to storage mode A/B or to storage mode A. Other changesof the storage mode may also be determined, such as to change anoperational parameter of the error coding dispersal storage function(e.g., number of pillars), which would revert the method to step 110.

FIG. 8 is a flowchart illustrating a method that begins at step 126where the DS processing module receives a data object from a source(e.g., a user device, the storage integrity processing unit, another DSprocessing unit, the DS unit, or the DS managing unit). The methodcontinues at step 128 where the DS processing module determines metadataassociated with the data object, which may be done in a similar manneras discussed with reference to step 108 of FIG. 7.

The method continues at step 130 where the DS processing moduledetermines a first dispersal method in a manner similar to step 110 ofFIG. 7. In addition, the DS processing module determines to store theslices in a DS units having a first type of memory (e.g., memory havinga first set of memory capabilities). The method continues at step 132where the DS processing module sends the slices to the DS units with thefirst memory type.

The method continues at step 134 where the DS processing unit determineswhether it is time to move the slices from the first type of memorydevice to a second type of memory device. Such a determination may bebased on one or more of, but not limited to, an elapsed time period ofstorage in the first type of memory, an elapsed time period since a dataslice retrieval from the first type of memory, a first type of memoryutilization indicator, a command, and/or a request. For example, theprocessing module may determine to transfer the plurality of data sliceswhen the processing module determines that the elapsed time period ofstorage in the first type of memory exceeds a storage threshold.

The method repeats at step 134 when it is not time to move the slices.When it is time to move the slices, the method continues at step 136where the DS processing module retrieves the slices from the DS unitshaving memory of the first memory type. The method then continues atstep 137 where the DS processing module determines whether toreconstruct data from the data slices. Such a determination may be basedon the type of data, the second memory type, a change in the storagerequirements (e.g., archiving, reduced retrieval needs, etc.), change inthe operational parameters of the error coding dispersal storagefunction, and/or any other factor that would require the data to bereconstructed.

When the data is to be reconstructed, the method continues at step 138the DS processing module reconstructs at least a portion of the datafrom the plurality of data slices in accordance with a first errorcoding dispersal function to produce reconstructed data. The first errorcoding dispersal function includes one or more of but not limited to anerror coding type that includes at least one of an error codingalgorithm, an encryption algorithm, and a compression algorithm andoperational parameters that include two or more of a pillar width, aread threshold, a slicing parameter, an integrity check method, acaching settings, and a parallelism settings.

The method continues to step 139 where the DS processing moduledetermines a second dispersal method (e.g., a second error codingdispersal storage function and identify the DS units having memory ofthe second type). The second error coding dispersal function includesone or more of, but not limited to, an error coding type that includesat least one of an error coding algorithm, an encryption algorithm, anda compression algorithm and operational parameters that include two ormore of a pillar width, a read threshold, a slicing parameter, anintegrity check method, a caching settings, and a parallelism settings.In an example, the second error coding dispersal function may includethe error coding type that is substantially the same as the error codingtype of the first error coding dispersal function. In another example,the second error coding dispersal function may include a different errorcoding type than that of the first error coding dispersal function. Inyet another example, the second error coding dispersal function mayinclude operational parameters that are substantially the same as theoperational parameters of the first error coding dispersal function. Infurther example, the second error coding dispersal function may includedifferent operational parameters than that of the first error codingdispersal function.

The method continues to step 140 where the DS processing module encodesthe reconstructed data into a second plurality of slices in accordancewith the second error coding dispersal storage function. The methodcontinues at step 142 from step 140 (or from step 137 when the data isnot to be reconstructed) where the DS processing module sends the slices(e.g., the original ones or the new ones) to DS units having memory ofthe second type. The method continues at step 144 where the DSprocessing module updates the virtual DSN address to physical locationtable to reflect where the slices are now stored. Note that the methodof FIG. 8 may be applied on a data segment by data segment basis or forgroup of data segments (e.g., a data file). In the latter case,pluralities of data slices may be processed to reconstruct the data(e.g., reconstruct the data file) and then the reconstructed data (e.g.,data file) is encoded to produce pluralities of slices encoded inaccordance with the second error coding dispersal storage function.

FIG. 9 is a schematic block diagram of an embodiment of a distributedstorage unit 146 (e.g., DS unit 36 &/or 94-104) that includes a storageunit control module 148, a plurality of memories of type A (1 througha), and a plurality of memories of type B (1 through b). The storageunit control module 148 includes the DSnet interface 150, an internalmemory for DS tables and logs 152, a memory for the operating system(OS) 154, and the DS processing 156. The storage unit control module 148may be operably coupled to the computing system via the DSnet interface150 via the network.

The memories, which may be implemented as part of or outside of the DSstorage unit 146, include one or more of a magnetic hard disk, NANDflash, read only memory, optical disk, and/or any other type ofread-only, and/or read/write memory. For example, memory A-1 may beimplemented in the DS unit 146 and memory A-2 may be implemented in aremote server (e.g., a different DS unit operably coupled to the DS unit146 via the network). In an example, memory A-1 through memory A-a areimplemented with the magnetic hard disk technology and memory B-1through memory B-b are implemented with the NAND flash technology.

The storage unit control module 148 receives EC data slices via theDSnet interface 150. Having received the slices, the storage unitcontrol module 148 determines where (e.g., which address on which of thememories) to store them. Such a determination may be based on one ormore of the metadata, a command (e.g., from the DS processing unitindicating which memory type to use), a type of data indicator, apriority indicator, available memory, memory performance data, memorycost data, and/or any other parameter to facilitate desired levels ofefficiency and performance. For example, the storage unit control module148 may choose memory A-1 (e.g., a magnetic hard disk drive) to storethe received EC data slice since the performance and efficiency is goodenough for the EC data slice requirements (e.g., availability, cost,response time).

Having determined where to store the slices, the storage unit controlmodule 148 updates and maintains a local virtual DSN address to physicalmemory table as part of the DS tables 152. The table maintains a recordof where the slices are physically stored in the memories and associatedthe physical location to the slice name.

The storage unit control module 148 may utilize DS processing 156 todistributedly store the DS tables, logs, and OS (e.g., that also utilizeinternal memory of the storage unit control module 148) to improve thereliability of operation of the DS unit 146. The DS unit 146 cansubsequently retrieve and restore one or more of the DS tables, logs,and OS. The storage unit control module 148 may determine when todistributedly store one or more of the DS tables, logs, and OS. Thedetermination may be based on one or more of a time period has expiredsince the last store, a command, an error message, a change in thememory architecture (e.g., a new memory device is added), and/or atleast one of the DS tables, logs, and OS have changed.

DS processing 156 may create EC data slices for the one or more of theDS tables, logs, and OS when the storage unit control module 148determines it is time to distributedly store one or more of the DStables, logs, and OS. The storage unit control module 148 may determinewhere to distributedly store the EC data slices. The determination maybe based on one or more of a predetermination, a command, a managementconfiguration parameter, a reliability indicator, a performance historyindicator, DSN memory architecture, and/or any other factor to optimizethe system reliability.

The storage unit control module 148 also determines where previouslystored EC data slices are located based on the local virtual DSN addressto physical memory table upon receiving a retrieve command via thenetwork. The storage unit control module 148 saves activity records(e.g., memory utilization, errors, stores, retrievals, etc.) as thelogs.

In an example, the storage unit control module 148 distributes theslices across the DS unit memories. In another example, the storage unitcontrol module 148 distributes k of the slices across memory B (for fastretrieval) and the other n−k slices across memory A. In yet anotherexample, the storage unit control module 148 distributes the slicesacross the DS unit memories and at least one other DS unit at the samesite as the DS unit 146. In yet another example, the storage unitcontrol module 148 distributes the slices across the DS unit memoriesand at least one other DS unit at a different site as the DS unit 146.

FIG. 10 is a flowchart illustrating the determination of a data storagemethod where the DS unit may choose the memory to store a new sliceand/or subsequently move a slice.

The DS unit receives the EC data slice and metadata from a sourceincluding one of the first type of user device, the storage integrityprocessing unit, the DS processing unit, another DS unit, or the DSmanaging unit 158. The DS processing unit (e.g., or another unit with DSprocessing) created the metadata associated with the data object aspreviously discussed.

The DS unit determines the memory requirements based on the metadata160. For example, the metadata may require very high reliability andfast retrieval speeds for the near term time period. The DS unit maysubsequently choose the memory that best matches those requirements.

The DS unit determines memory availability and memory characteristicsbased on stored information in the DS tables 162. The DS unit determinesthe storage mode based on the memory requirements and the memoryavailability and memory characteristics 164. The storage mode mayinclude the memory selection and a time phase indicator. The time phasemay include a first phase to include the time period between the initialstorage of the new slice until the time when the storage mode is to bere-evaluated. Other time phases may comprise a subsequent phase toinclude the time period between the last storage mode re-evaluationuntil the time when the storage mode is to be re-evaluated. For example,the DS unit determines the storage mode to be a B mode (e.g., fastreliable yet costly solid state memory) for the first time phase afterthe initial slice storage when subsequent retrievals may be frequent.The DS unit updates the local virtual DSN address to physical locationtable to reflect where the slices will be stored.

The DS unit utilizes the current storage mode to store new slices inmemory or to move the data of slices from one memory to another when thestorage mode has changed 166. The DS unit looks up the mapping in thelocal virtual DSN address to physical location table to determine wherethe slices should be stored. Note that the local virtual DSN address tophysical location table may include both the current storage mode andthe last storage mode to facilitate moving slices from the memory of thelast mode to the memory in accordance with the current storage mode.

The DS unit may store all n slices of each data segment for storage tomemory type B when the storage mode is the B mode 168. Note that thisscenario may include the metadata-indicated requirement for fast access(even with failures), highly reliable memory with no cost constraint forthe current time phase.

The DS unit may store k slices of each data segment for storage tomemory type B 170 and the other n−k slices to memory type A 172 when thestorage mode is an A/B mode. Note that this scenario may include themetadata-indicated requirement for fast access (without failures),reliable memory with some cost constraint for the current time phase.Further note that the DS unit need only retrieve the n−k slices from theslower memory A if at least one of the memory B devices fails. In otherwords, the A/B mode may offer a compromise of retrieval speed and cost.

The DS unit may send all n slices of each data segment for storage tomemory type A when the storage mode is the A mode 174. Note that thisscenario may include the metadata-indicated requirement for routineinfrequent access, normally reliable memory with cost constraints forthe current time phase. Note that this storage mode scenario may alignwith better with the archive storage of data for long periods betweenretrievals.

The DS unit may first retrieve the slices from the memory of the DS unitand from other DS units (e.g., determining where the slices are at byaccessing the virtual DSN address to physical location table) asindicated by the last storage mode in order to recreate the data objectsuch that slices may be created in accordance with the current storagemode in each of the above three storage mode scenarios when it is timeto change the storage mode for previously stored slices.

The DS unit determines if it is time to reassess the storage mode 176.The determination may be based on one or more of a time period haselapsed since the current storage mode, there have been no retrievals ofthe slice within a time period, a command, a request, and/or a memorytype is filling up (e.g., memory B). Note that a very likely scenario isstarting with the B mode, transition to the A/B mode, and thentransition and remain at the A mode for a longer period of time. Thescenario may align with the requirement to retrieve the slice often atfirst and less often as time goes on. Note that in a future scenario,the storage mode may transition from the A mode to the A/B mode or evento the B mode when the requirements for previously stored slices changesto require more frequent retrievals with very high reliability.

The DS unit moves to the step to determine the storage mode 164 when theDS unit determines if it is time to reassess the storage mode. The DSunit moves to the step to utilize the current storage mode 166 when theDS unit determines it is not time to reassess the storage mode.

In another embodiment of the computing system 10, the computing systemincludes one or more of but not limited to a processing module 50, amain memory 54, dispersal memory interface 32 (e.g., a multi-generalpurpose input output and/or a plurality of interfaces), a local non-mainmemory (e.g., a hard disk memory, a flash memory, etc. that is closelyassociated with a computing core 26), and/or a non-local non-main memory36 (e.g., memory of a DSN unit). For example, the processing module 50may be implemented as a dispersed storage processing unit and the mainmemory 54, the local non-main memory, and/or the non-local non-mainmemory 36 may comprise a plurality of memory devices associated with aDS unit. Note that each of the main memory 54, the local non-mainmemory, and the non-local non-main memory 36 comprises memory deviceswhere the memory devices may be associated with one or more memorydevice capabilities. Memory device capabilities may include one or moreof but not limited to a memory device storage cost, a memory devicestorage access speed, memory device storage reliability, memory devicestorage availability, and/or a memory device storage capacity.

In an example of operation, the DS unit comprises and interface module,a plurality of memory devices, and a dispersed storage processing unitthat, in an embodiment, operates in accordance with the method describedbelow. The method begins with the step where the DS processing unit ofthe DS unit has DS unit operational data and/or a DS unit operatingsystem algorithm to store. The DS unit operational data may include oneor more of but not limited to a DS table, a local virtual distributedstorage network (DSN) address to physical memory table, a log, anactivity record, a memory utilization record, an error record, a storagerecord, a retrieval record, and/or a vault information record. In otherwords, the DS unit operational data may be data that is used from timeto time to operate the DS unit. The DS unit operating system algorithmmay include at least a portion of operating system executable softwarethat is utilized to operate the DS unit.

The method continues with the step where the DS processing unit Encodesat least a portion of the at least one of DS unit operational data andDS unit operating system algorithm in accordance with an error codingdispersal storage function to produce a plurality of data slices. In anembodiment, the dispersed storage processing unit selects at least oneof the plurality of memory devices by determining memory devicerequirements based in part on metadata and identifying the memorydevices based on the memory device requirements. The metadata mayinclude one or more of but not limited to a data type, a data size, adata priority, a data security index, an estimated storage time, anestimated time between retrievals, a storage requirement. For example,the dispersed storage processing unit may select a memory device basedon a fast access for a first time period memory device requirement whenthe dispersed storage processing unit determines the first time periodmemory device requirements based on the metadata that indicates ashorter than average estimated time between retrievals for theassociated data.

The method continues with the step where the DS processing unit storesat least some of the plurality of data slices in memory devices of theDS unit in accordance with the error coding dispersal storage function.In an embodiment, the DS processing unit stores at least a readthreshold number of the plurality of data slices in a first set of thememory devices (e.g., a number of pillars great than or equal to theread threshold), and stores the remaining data slices of the pluralityof data slices (e.g., the rest of the pillars) in a second set of thememory devices. In an example, the first set of memory devices providesfast access while the second set of memory devices provides reliability.

In another embodiment, the DS processing unit stores at least some ofthe plurality of data slices in memory devices of the DS unit and sendsat least a remaining one of the plurality of data slices to a memorydevice of another DS unit in accordance with the error coding dispersalstorage function. In other words, the DS processing unit stores at leastone pillar of slices in a different DS unit. In an example, the DSprocessing unit stores the read threshold number of pillars in the DSunit and the remaining pillars in a different DS unit to provide areliability improvement to the system.

In another example of operation, the DS processing unit of the DS unitreceives an encoded slice to store. The method begins with the stepwhere the DS processing unit selects one of the plurality of memorydevices for storing the encoded slice based on metadata associated withthe encoded slice to produce a selected memory device. In anotherembodiment, the DS processing unit selects one of the memory devices ofthe DS unit by retrieving data slices of the DS unit operational datafrom the memory devices to produce retrieved data slices, reconstructingvault information from the retrieved data slices in accordance with theerror coding dispersal storage function, and selecting the one of thememory devices based on the vault information. In other words, the DSprocessing unit retrieves operational data store the slices to determinewhere to store the encoded slice. The DS processing unit of the DS unitstores the encoded slice in the selected memory device.

In another example of operation, the DS unit comprises and interfacemodule, a plurality of memory devices, and a processing unit that, in anembodiment, operates in accordance with the method described below. Themethod begins with the step where the processing unit of the DS unitreceives, via the interface module, an encoded slice of content data.For example, the DS unit may receive an encoded slice from a user devicefor storage in the DS unit. The processing unit determines that theencoded slice is to be stored as the encoded slice may have beenreceived with a store slice command. The processing unit retrieves aplurality of data slices from at least some of the plurality of memorydevices based on the encoded slice. In other words, the processing unitretrieves the plurality of data slices that are associated with theencoded slice such as a vault identity.

The method continues with the step where the processing unitreconstructs DS operational data from the plurality of data slices inaccordance with an error coding dispersal storage function. The DSoperational data may include one or more of but not limited to a DStable, a local virtual distributed storage network (DSN) address tophysical memory table, a log, an activity record, a memory utilizationrecord, an error record, a storage record, a retrieval record, a vaultinformation record.

The method continues with the step where the processing unit selects oneof the plurality of memory devices for storing the encoded slice basedon the DS operational data. In other words, the DS operational data mayinclude a table that identifies memory devices associated with theencoded slice. The processing unit stores the encoded slice in theselected memory device.

In another example of operation, the processing unit retrieves aplurality of data slices of a DS unit operating system algorithm from atleast some of the plurality of memory devices, reconstructs the DS unitoperating system algorithm from the plurality of data slices inaccordance with an error coding dispersal storage function, and executesat least a portion of the DS unit operating system algorithm.

In another example of operation, the processing unit updates the DSoperational data to produce updated DS operational data when the encodedslice is stored by constructing a second plurality of data slices fromthe updated DS operational data in accordance with the error codingdispersal storage function, sending, via the interface module, thesecond plurality of data slices to at least some of the plurality ofmemory devices for storage based on the encoded slice.

FIG. 11 is a flowchart illustrating the management of a memory devicewhere the DS unit may power down a memory device that is not utilizedoften to extend the operational life of the memory device.

The DS unit receives the EC data slice and metadata from a sourceincluding one of the first type of user device, the storage integrityprocessing unit, the DS processing unit, another DS unit, or the DSmanaging unit 178. The DS processing unit (e.g., or another unit with DSprocessing) created the metadata associated with the data object aspreviously discussed.

The DS unit determines the memory requirements based on the metadata180. For example, the metadata may require very high reliability andfast retrieval speeds for the near term time period. In another example,the metadata may require a very long period of storage with fewretrievals (e.g., records archive). The DS unit may subsequently choosethe memory that best matches those requirements.

The DS unit determines memory availability and memory characteristicsbased on stored information in the DS tables 182. The DS unit determinesthe storage mode based on the memory requirements and the memoryavailability and memory characteristics 184. The storage mode mayinclude the memory selection and a time phase indicator. The time phasemay include a first phase to include the time period between the initialstorage of the new slice until the time when the memory is to be poweredoff. Other time phases may comprise a subsequent phase to include thetime period between the last power down until the time when the memorypower is to be turned back on to perform memory tests. For example, theDS unit determines the storage mode to be a long term archive after aten day first time phase after the initial slice storage when subsequentretrievals may be frequent. The DS unit updates the local virtual DSNaddress to physical location table to reflect where the slices will bestored.

The DS unit utilizes the current storage mode to store new slices inmemory 186. The DS unit looks up the mapping in the local virtual DSNaddress to physical location table to determine where the slices shouldbe stored.

The DS unit determines when to turn off the memory based on one or moreof the first time phase period has expired after the initial store, acommand, a predetermined value, a irregular power indicator, anearthquake indicator, a bad weather indicator, a retrieval frequencyindicator, and/or any other indicator to improve the life of the memorydevice 188. The DS unit powers down the memory when the DS unitdetermines to turn off the memory.

The DS unit determines when to turn on the memory based on one or moreof the other time phase has expired since the memory was powered down, acommand, a predetermined value, a irregular power indicator, anearthquake indicator, a bad weather indicator, a retrieval frequencyindicator, and/or any other indicator to improve the life of the memorydevice 190. The memory may be powered up to perform integrity andconsistency checks of the stored slices.

The DS unit turns on the memory when the DS unit determines to turn onthe memory. The DS unit determines failed memory and checks for sliceinconsistency when the memory is turned on 192. The failed memorydetermination is based on an operational test of the memory device(e.g., go, no-go). The slice inconsistency test checks for missing orold slices (e.g., including comparing slice name lists and versions toother pillars of a same storage group) and/or slices with errors (e.g.,as indicated by a mismatch between the stored checksum and the presentlycalculated checksum over the slice). The DS unit returns to the step todetermine when to turn the memory off when the DS unit does not detectany errors 188.

The DS unit determines when to rebuild the slices with errors when theDS unit detects errors 194. The determination may be based on one ormore of memory device availability (e.g., may be waiting for areplacement hard disk drive to be installed), a command, a timer, and/ora substitute memory becoming available.

The DS unit rebuilds and stores the recreated slice when the DS unitdetermines that it is time to rebuild the slices 196. The DS unitretrieves the good slices of the same segment from the other pillar DSunits, de-slices, and decodes to produce the original data object. TheDS unit recodes and re-slices the original data object to producerepaired slices for the one or more slices that were in error. The DSunit stores the repaired slices in the DS unit memory and updates thelocal virtual DSN address to physical location table if there are anychanges (e.g., when a substitute memory is utilized).

In another embodiment of the computing system 10, the computing systemincludes one or more of but not limited to a processing module 50, amain memory 54, dispersal memory interface 32 (e.g., a multi-generalpurpose input output and/or a plurality of interfaces), a local non-mainmemory (e.g., a hard disk memory, a flash memory, etc. that is closelyassociated with a computing core 26), and/or a non-local non-main memory36 (e.g., memory of a DSN unit). For example, the processing module 50may be implemented as a dispersed storage processing unit and the mainmemory 54, the local non-main memory, and/or the non-local non-mainmemory 36 may comprise a plurality of memory devices associated with aDS unit. Note that each of the main memory 54, the local non-mainmemory, and the non-local non-main memory 36 comprises memory deviceswhere the memory devices may be associated with one or more memorydevice capabilities. Memory device capabilities may include one or moreof but not limited to a memory device storage cost, a memory devicestorage access speed, memory device storage reliability, memory devicestorage availability, and/or a memory device storage capacity.

In an example of operation, the DS unit comprises and interface module,a plurality of memory devices, and a processing unit that, in anembodiment, operates in accordance with the method described below. Theplurality of memory devices includes a first set of memory devices thatare continually active and a second set of memory devices that areselectively active, wherein the first set of memory devices store firstdata having a rate of retrieval in a first interval retrieval rate rangeand the second set of memory devices store second data having a rate ofretrieval in a second interval retrieval rate range. For example, thefirst set of memory devices may be utilized when data is retrieved at ahigher rate than the data retrieved from the second set of memorydevices. In an instance, data is archived utilizing the second set ofmemory devices followed such that at least one memory device of thesecond set of memory devices may be de-activated from time to time. Notethat the de-activation of a memory device may provide the system with areliability improvement and/or power savings.

In an embodiment, the processing unit of the DS unit may re-activate amemory device of the second set of memory devices from time to time todetermine if the data that was archived in the memory device is stillerror free. The method to determine if the data is still error freebegins with the step where the processing unit of the DS unit determineswhen to activate a memory device of the second set. In an embodiment,the processing unit determines when to activate the memory device of thesecond set based on one or more of but not limited to a retrievalrequest for at least a portion of the second data, elapsed inactivestate time of the memory device of the second set, a command, anirregular power indicator, an earthquake indicator, a bad weatherindicator, a retrieval frequency indicator, and/or an indicator toimprove the life of the memory device.

The method continues with the step where the processing unit activatesthe memory device to produce an activated memory device when the memorydevice is to be activated. The processing unit retrieves sliceinformation from the activated memory device to produce a retrievedencoded slice and/or slice information where the slice information mayinclude one or more of but not limited to an encoded slice, contentdata, error control information, a hash of a slice name list, a slicename list, a source name list, a hash of a source name list, and/or aslice revision.

The method continues with the step where the processing unit determineswhether the retrieved encoded slice has an error. The determination maybe based on one or more of but not limited to a missing slice test, anoutdated slice revision test, a slice name comparison to at least oneother slice name from a slice name list, a slice revision comparison toat least one other slice revision from a slice revision list, a slicename comparison to at least one other slice name from another DS unit, aslice revision comparison to at least one other slice revision fromanother DS unit, and/or a stored checksum comparison to a re-calculatedchecksum.

In an embodiment, the method continues with the step where theprocessing unit initiates a rebuilding function to rebuild the retrievedencoded slice producing a rebuilt encoded slice when the processing unitdetermines that the retrieved encoded slice has an error. The processingunit stores the rebuilt encoded slice in the activated memory device andmay de-activate the activated memory device (e.g., right away or on adelayed basis).

In an embodiment, the method continues with the step where theprocessing unit determines a condition for activating the memory devicewhen the retrieved encoded slice does not have an error. In other words,the processing unit determines why the memory device was activated(e.g., to check for errors and/or to retrieve an encoded slice). Theprocessing unit sends, via an interface module, the retrieved encodedslice and initiates deactivation of the memory device when the conditionwas a data access request (e.g., to retrieve and encoded slice). Theprocessing unit initiates the deactivation of the memory device when thecondition was verification-based (e.g., to check for errors).

In another embodiment, the processing unit determines when tode-activate the memory device and the processing unit de-activates thememory device to produce a de-activated memory device when the memorydevice is to be de-activated. The determination may be based on one ormore of but not limited to elapsed time since a retrieval request for atleast a portion of the second data, elapsed time since a store requestfor at least a portion of the second data, elapsed active state time ofthe memory device, a command, an irregular power indicator, anearthquake indicator, a bad weather indicator, a retrieval frequencyindicator, and/or an indicator to improve the life of the memory device.

In an example of operation, the DS unit receives an encoded slice forstorage. The method begins with the step where the processing unitdetermines whether to store the encoded slice in one of the first set ofmemory devices or in one of the second set of memory devices based onmetadata associated with the encoded slice. The metadata may include oneor more of but not limited to a data type, a data size, a data priority,a data security index, a reliability indicator, a performance indicator,an estimated storage time, an estimated time between retrievals, and/ora storage requirement. For example, the processing unit may store theencoded slice in the one of the first set of memory devices when theencoded slice has a first retrieval likelihood (e.g., more often thatthe second). In another example, the processing unit may store theencoded slice in the one of the second set of memory devices when theencoded slice has a second retrieval likelihood (e.g., less often thanthe first such as an archiving).

The method continues with the step where the processing unit stores theencoded slice in the one of the second set of memory device when theencoded slice is to be stored in the one of the second set of memorydevices. The processing unit may de-activate the one of the second setof memory devices, in accordance with a deactivation protocol, afterstoring the encoded slice. The deactivation protocol may include one ormore of but not limited to elapsed time since storing the encoded slicein the one of the second set of memory devices, elapsed time since aretrieval request for the encoded slice, elapsed active state time ofthe one of the second set of memory devices, a command, an irregularpower indicator, an earthquake indicator, a bad weather indicator, aretrieval frequency indicator, and/or an indicator to improve the lifeof the memory device.

In another embodiment, the processing unit stores the encoded slice inthe one of the first set of memory devices when the encoded slice is tobe stored in the one of the first set of memory devices. The processingunit may determine whether to transfer the encoded slice from the one ofthe first set of memory devices to the one of the second set of memorydevices based a data transfer protocol (e.g., how much time later, acondition of transfer etc.). For example, the processing unit maydetermine to transfer the encoded slice when a time period has elapsedits initial storage of the encoded slice in the one of the first set ofmemory devices. The processing unit may retrieve the encoded slice fromthe one of the first set of memory devices and store the encoded slicein the one of the second set of memories when the processing unitdetermines that the encoded slice is to be transferred.

As may be used herein, the terms “substantially” and “approximately”provides an industry-accepted tolerance for its corresponding termand/or relativity between items. Such an industry-accepted toleranceranges from less than one percent to fifty percent and corresponds to,but is not limited to, component values, integrated circuit processvariations, temperature variations, rise and fall times, and/or thermalnoise. Such relativity between items ranges from a difference of a fewpercent to magnitude differences. As may also be used herein, theterm(s) “coupled to” and/or “coupling” and/or includes direct couplingbetween items and/or indirect coupling between items via an interveningitem (e.g., an item includes, but is not limited to, a component, anelement, a circuit, and/or a module) where, for indirect coupling, theintervening item does not modify the information of a signal but mayadjust its current level, voltage level, and/or power level. As mayfurther be used herein, inferred coupling (i.e., where one element iscoupled to another element by inference) includes direct and indirectcoupling between two items in the same manner as “coupled to”. As mayeven further be used herein, the term “operable to” indicates that anitem includes one or more of power connections, input(s), output(s),etc., to perform one or more its corresponding functions and may furtherinclude inferred coupling to one or more other items. As may stillfurther be used herein, the term “associated with”, includes directand/or indirect coupling of separate items and/or one item beingembedded within another item. As may be used herein, the term “comparesfavorably”, indicates that a comparison between two or more items,signals, etc., provides a desired relationship. For example, when thedesired relationship is that signal 1 has a greater magnitude thansignal 2, a favorable comparison may be achieved when the magnitude ofsignal 1 is greater than that of signal 2 or when the magnitude ofsignal 2 is less than that of signal 1.

The present invention has also been described above with the aid ofmethod steps illustrating the performance of specified functions andrelationships thereof. The boundaries and sequence of these functionalbuilding blocks and method steps have been arbitrarily defined hereinfor convenience of description. Alternate boundaries and sequences canbe defined so long as the specified functions and relationships areappropriately performed. Any such alternate boundaries or sequences arethus within the scope and spirit of the claimed invention.

The present invention has been described above with the aid offunctional building blocks illustrating the performance of certainsignificant functions. The boundaries of these functional buildingblocks have been arbitrarily defined for convenience of description.Alternate boundaries could be defined as long as the certain significantfunctions are appropriately performed. Similarly, flow diagram blocksmay also have been arbitrarily defined herein to illustrate certainsignificant functionality. To the extent used, the flow diagram blockboundaries and sequence could have been defined otherwise and stillperform the certain significant functionality. Such alternatedefinitions of both functional building blocks and flow diagram blocksand sequences are thus within the scope and spirit of the claimedinvention. One of average skill in the art will also recognize that thefunctional building blocks, and other illustrative blocks, modules andcomponents herein, can be implemented as illustrated or by discretecomponents, application specific integrated circuits, processorsexecuting appropriate software and the like or any combination thereof.

What is claimed is:
 1. A method for dispersed memory storage comprises:receiving data for storage; determining storage metadata regardingstorage requirements of the data, wherein the storage metadataindicating one or more of: a set of storage units of a plurality of setsof storage units of a dispersed storage network (DSN) memory, a storagemode of a plurality storage modes, and a corresponding one of aplurality of error coding dispersal storage functions; encoding a datasegment of the data in accordance with the corresponding one of aplurality of error coding dispersal storage functions to produce a setof encoded data slices; when the storage metadata indicates a first typeof storage mode of the plurality of storage modes: outputting the set ofencoded data slices to a first set of memory devices of the set ofstorage units for storage therein; determining to change the storagemode from the first type of storage mode to a third type of storage modeof the plurality of storage modes after outputting the set of encodeddata slices to the first set of memory devices of the set of storageunits for storage; and facilitating transfer of a subset of encoded dataslices of the set of encoded data slices from storage in the first setof memory devices to storage in a subset of a second set of memorydevices, wherein a set difference of the set of encoded data slices andthe subset of the set of encoded data slices is greater than or equal toa decode threshold number of the one of the plurality of error codingdispersal storage functions; when the storage metadata indicates asecond type of storage mode of the plurality of storage modes:outputting the set of encoded data slices to the second set of memorydevices of the set of storage units of the DSN memory for storagetherein; and when the storage metadata indicates the third type ofstorage mode of the plurality of storage modes: outputting the decodethreshold number of encoded data slices of the set of encoded dataslices to a subset of the first set of memory devices for storagetherein; and outputting remaining encoded data slices of the set ofencoded data slices to the subset of the second set of memory devicesfor storage therein.
 2. The method of claim 1 further comprising: thefirst type of storage mode including a first time phase indicator thatspecifies a time period for initial storage of the data; and the secondtype of storage mode including a second time phase that corresponds to atime period after the time period for initial storage of the dataexpires.
 3. The method of claim 1 further comprises: the first type ofstorage mode including an indication for customized data content; andthe second type of storage mode including an indication for generic datacontent.
 4. The method of claim 1 further comprises: the first type ofstorage mode including at least one of a first retrieval requirement anda first reliability requirement; and the second type of storage modeincluding at least one of a second retrieval requirement and a secondreliability requirement.
 5. The method of claim 1, wherein the DSNmemory comprises: a plurality of DSN memory sites, wherein a one of theplurality of DSN memory sites includes a dispersed storage (DS) unitthat includes a first type of memory devices and a second one of theplurality of DSN memory sites includes a DS unit that includes a secondtype of memory devices, wherein the first type of memory devices havedifferent memory characteristics than the second type of memory devices,and wherein the memory characteristics includes one or more of: speed ofaccess, cost, reliability, availability, and capacity.
 6. The method ofclaim 1, wherein the DSN memory comprises: a plurality of dispersedstorage (DS) units, wherein the first memory includes a first set of theplurality of DS units and the second memory includes a second set of theplurality of DS units, wherein one of the plurality of DS units includesa first type of memory devices and a second type of memory devices,wherein the first type of memory devices have different memorycharacteristics than the second type of memory devices, and wherein theone of the plurality of DS units is included in the first and second setof the plurality of DS units.
 7. The method of claim 1, whereindetermining to change the storage mode from the first type of storagemode to the third type of storage mode is based on determining a timeperiod of storage in the first set of memory devices has elapsed.
 8. Themethod of claim 1, wherein determining to change the storage mode fromthe first type of storage mode to the third type of storage mode isbased on determining an update of the storage metadata has occurred. 9.The method of claim 1, wherein determining to change the storage modefrom the first type of storage mode to the third type of storage mode isbased on determining a change of available memory devices has occurred.10. The method of claim 1, further comprising, when the storage metadataindicates the third type of storage mode of the plurality of storagemodes: determining to change the storage mode from the third type ofstorage mode to the second type of storage mode after outputting thedecode threshold number of encoded data slices of the set of encodeddata slices to the subset of the first set of memory devices for storageand after outputting the remaining encoded data slices of the set ofencoded data slices to the subset of the second set of memory devicesfor storage therein; and facilitating transfer of the decode thresholdnumber of encoded data slices of the decode threshold number of encodeddata slices from storage in the first set of memory devices to storagein the second set of memory devices.
 11. A computer comprises: adispersal memory interface; and a processing module operable to: receivedata for storage; determine storage metadata regarding storagerequirements of the data, wherein the storage metadata indicating one ormore of: a set of storage units of a plurality of sets of storage unitsof a dispersed storage network (DSN) memory, a storage mode of aplurality storage modes, and a corresponding one of a plurality of errorcoding dispersal storage functions; encode a data segment of the data inaccordance with the corresponding one of a plurality of error codingdispersal storage functions to produce a set of encoded data slices;when the storage metadata indicates a first type of storage mode of theplurality of storage modes: output the set of encoded data slices to afirst set of memory devices of the set of storage units for storagetherein; determine to change the storage mode from the first type ofstorage mode to a third type of storage mode of the plurality of storagemodes after outputting the set of encoded data slices to the first setof memory devices of the set of storage units for storage; andfacilitate transfer of a subset of encoded data slices of the set ofencoded data slices from storage in the first set of memory devices tostorage in a subset of a second set of memory devices, wherein a setdifference of the set of encoded data slices and the subset of the setof encoded data slices is greater than or equal to the decode thresholdnumber of the one of the plurality of error coding dispersal storagefunctions; when the storage metadata indicates a second type of storagemode of the plurality of storage modes: output the set of encoded dataslices to a second set of memory devices of the set of storage units forstorage therein; and when the storage metadata indicates the third typeof storage mode of the plurality of storage modes: output the decodethreshold number of encoded data slices of the set of encoded dataslices to a subset of the first set of memory devices for storagetherein; and output remaining encoded data slices of the set of encodeddata slices to the subset of the second set of memory devices forstorage therein.
 12. The computer of claim 11 further comprises: thefirst type of storage mode including a first time phase indicator thatspecifies a time period for initial storage of the data; and the secondtype of storage mode including a second time phase that corresponds to atime period after the time period for initial storage of the dataexpires.
 13. The computer of claim 11 further comprises: the first typeof storage mode including an indication for customized data content; andthe second type of storage mode including an indication for generic datacontent.
 14. The computer of claim 11 further comprises: the first typeof storage mode including at least one of a first retrieval requirementand a first reliability requirement; and the second type of storage modeincluding at least one of a second retrieval requirement and a secondreliability requirement.
 15. The computer of claim 11, wherein the DSNmemory comprises: a plurality of DSN memory sites, wherein a one of theplurality of DSN memory sites includes a dispersed storage (DS) unitthat includes a first type of memory devices and a second one of theplurality of DSN memory sites includes a DS unit that includes a secondtype of memory devices, wherein the first type of memory devices havedifferent memory characteristics than the second type of memory devices,and wherein the memory characteristics includes one or more of: speed ofaccess, cost, reliability, availability, and capacity.
 16. The computerof claim 11, wherein the DSN memory comprises: a plurality of dispersedstorage (DS) units, wherein the first memory includes a first set of theplurality of DS units and the second memory includes a second set of theplurality of DS units, wherein one of the plurality of DS units includesa first type of memory devices and a second type of memory devices,wherein the first type of memory devices have different memorycharacteristics than the second type of memory devices, and wherein theone of the plurality of DS units is included in the first and second setof the plurality of DS units.
 17. The computer of claim 11, whereindetermining to change the storage mode from the first type of storagemode to the third type of storage mode is based on determining a timeperiod of storage in the first set of memory devices has elapsed. 18.The computer of claim 11, wherein determining to change the storage modefrom the first type of storage mode to the third type of storage mode isbased on determining an update of the storage metadata has occurred. 19.The computer of claim 11, wherein determining to change the storage modefrom the first type of storage mode to the third type of storage mode isbased on determining a change of available memory devices has occurred.20. The computer of claim 11, wherein the processing module, when thestorage metadata indicates the third type of storage mode of theplurality of storage modes, is further operable to: determine to changethe storage mode from the third type of storage mode to the second typeof storage mode after outputting the decode threshold number of encodeddata slices of the set of encoded data slices to the subset of the firstset of memory devices for storage and after outputting the remainingencoded data slices of the set of encoded data slices to the subset ofthe second set of memory devices for storage therein; and facilitatetransfer of the decode threshold number of encoded data slices of thedecode threshold number of encoded data slices from storage in the firstset of memory devices to storage in the second set of memory devices.